Local storage, that is, storage associated with, for example, a processing unit as opposed to the main storage component of a data processing system has typically been accessed in a manner which is singular in nature, that is, one line of storage at a time. Thus, if an array of memory chips are presented with an address, a logically contiguous line is retrieved from that memory. However, it has been recognized in the prior art that it is desirable to have the capability of reading from two lines of local storage simultaneously. This capability has been achieved through the provision of parallel local stores with separate accessing means, each one to provide a line of storage simultaneously on one read operation. Obviously such an arrangement is an expensive solution.
It is, therefore, the primary object of this invention to provide simultaneous addressing to different locations in a single local storage unit so that the total data read from the local store at a single access is composed partly of data bytes from one storage location and partly of data bytes from another storage location. The advantages of such an arrangement are many. One of the major uses of local storage is to store data and addresses which normally would be found in main storage for convenient use within the processor unit. System design has made local storage arrangements profitable because of the time needed to get out of processor data flow and into memory data flow. Where local storage is used to contain main storage addresses it is frequently the case that the main storage address consists of a segment name, for example the name of a control block, and the displacement within that control block to particular data. Thus, to access that particular data, the address read from the local store will consist of the segment name and the displacement. If the addresses of all the particular data in a control block are located in local store, the segment name will be repeated line after line after line with only the displacement value changing in each of these address expressions. Through use of the current invention the segment name may be addressed in a single line and only the displacement address in one of several additional lines, thus creating space on those additional lines which may be used for other purposes. As a result local storage, when arranged according to the present invention, will be available for additional uses.